Missing Documentation for 8.x

[mahalakshme]

AC:

Below for implementers:

• Being able to access user and myGroups in all rules avni-client#1334 - As part of this card - user and myUserGroups accessible in all rules from mobile app. But in readme it is added only for report card rule and edit form rule. Like we have common imports, add common params as well in the top if you think that will suffice.
• Add some documentation for WFA, HFA, WFH and BMI for age covering the below:
  1. we use WHO standards(formula, LMS values)
  2. for whom it is intended(BMI for adoloscents, others are for children less than x(i think less than 5 only we support - cross check) years of age
  3. how to invoke
• Add documentation for secondary dashboard (Add dashboard shortcut to bottom drawer avni-client#1328)
  1. How to configure
  2. Some nuances like can we make different dashboards as secondary/primary dashboard in different user groups(to which a user belongs to) and if we can what will happen
  3. How it will display in mobile app
  4. Also link this to the documentation added here

[himeshr]

Code review changes made in below places as per AC:

https://avni.readme.io/docs/writing-rules#shape-of-common-params-object
https://avni.readme.io/docs/child-growth-charts
https://avni.readme.io/docs/user-groups
https://avni.readme.io/docs/offline-reports